Why Redford's performance here is his best
Because he's not acting...he's reacting. He's not being showy or melodramatic, but real. He's not trying to impress, but performs with sheer naturalism. Its an intimate movie where Redford has us in his grasp every minute of it and doesn't need to say a word because we can read everything he's thinking on his face. It was a physically and emotionally gruelling role that he performed perfectly.
Robert Redford is "our man."